Method for measuring blade cross-section profile based on line structured-light sensor at high precision

ABSTRACT

The present disclosure provides a method for measuring a blade cross-section profile based on a line structured-light sensor at a high precision, including: (10) pose calibration on a line structured-light sensor; (20) calibration on a rotation axis: calibrating the rotation axis with a lateral datum plane of a blade; and (30) cross-section profile measurement on a target measured blade: establishing a global coordinate system, and converting blade cross-section curve feature data acquired by a data coordinate system to the coordinate system for splicing, thereby measuring a blade cross-section profile. The present disclosure reduces the error arising from transfer of calibration objects, reduces the rotation error because it does not involve the rotation angle of the turntable when calibrating the rotation axis and the rotation center, and reduces the translational error of the line structured-light sensor as positions for rotating the line structured-light sensor in two times are unchanged.

CROSS REFERENCE TO RELATED APPLICATION

This patent application claims the benefit and priority of ChinesePatent Application No. 202011128989.6, filed on Oct. 21, 2020, thedisclosure of which is incorporated by reference herein in its entiretyas part of the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure belongs to the field of blade profilemeasurement, and in particular, relates to a method for measuring ablade cross-section profile based on a line structured-light sensor at ahigh precision.

Description of the Related Art

Blades are core components of aviation engines, gas turbines, steamturbines and other devices, and play a vital role in conversion fromheat energy to mechanical energy. The profile and quality of the bladesdirectly affect the energy conversion efficiency and service life of thecomplete machines. The blades are difficulty to be measured because thecross sections are irregularly free-from surfaces and each cross-sectionprofile is different.

A Chinese invention patent 201911267259.1 discloses a method formeasuring a blade based on a line structured-light sensor. Themeasurement method includes: (1) calibration on a measurement apparatusbefore blade installation: calibrating moving axes X and Y of a linestructured-light sensor, calibrating a moving axis Z with a rectangularcalibration block, and calibrating a turntable plane with an angularsensor; (2) calibration on a blade axis after the blade installation,and calibration on the blade axis with blade datum planes A and B (twolateral datum planes); and (3) measurement on a target measured blade.The method calibrates a rotation axis with the angular sensor and thecurve feature of the blade, and overcomes the transfer error arisingfrom a conventional criterion sphere. However, with cumbersome operationsteps, the method is not applicable to measuring blade cross-sectioncurve having large curvatures, and has the large measurement errors.

BRIEF SUMMARY OF THE INVENTION

An objective of the present disclosure is to provide a method formeasuring a blade cross-section profile based on a line structured-lightsensor at a high precision, which is simple in operation and applicableto measuring various blades.

A method for measuring a blade cross-section profile based on a linestructured-light sensor at a high precision includes the followingsteps:

(10) pose calibration on a line structured-light sensor: calibrating X,Y and Z axes of a moving coordinate system, such that a data coordinatesystem o-xyz of the line structured-light sensor is parallel to themoving coordinate system O-XYZ;

(20) calibration on a rotation axis: calibrating the rotation axis of aturntable, such that a blade axis is parallel to the rotation axis; and

(30) cross-section profile measurement on a target measured blade:establishing a global coordinate system, and converting bladecross-section curve feature data acquired by the data coordinate systemto the coordinate system for splicing, thereby measuring a bladecross-section profile;

where the calibration on a rotation axis in step (20) includes thefollowing steps:

(21) putting the target measured blade onto the turntable, and adjustinga pose of the line structured-light sensor such that a laser plane ofthe line structured-light sensor intersects with a lateral datum planeof the blade, the line structured-light sensor acquiring profile pointdata M₁ of the datum plane;

(22) ensuring that the pose of the line structured-light sensor isunchanged, and the line structured-light sensor acquires profile pointdata M₂ of a lateral datum plane after rotation of the turntable; androtating the turntable again and ensuring that the pose of the linestructured-light sensor is unchanged, and the line structured-lightsensor acquires profile point data M₃ of the lateral datum plane, wherethe lateral datum planes in step (21) and step (22) are the same datumplane;

(23) fitting the data M₁, M₂ and M₃ linearly to obtain three straightlines L₁, L₂ and L₃, and solving, according to equal distances from arotation center point O₁ to the three straight lines L₁, L₂ and L₃, therotation center point O₁;

(24) moving the line structured-light sensor along the Z-axis of themoving coordinate system, such that the laser plane of the linestructured-light sensor intersects with the lateral datum plane of theblade, and repeating steps (21)-(23) to obtain a rotation center pointO₂; and

(25) solving a space linear equation of the rotation axis through therotation center points O and O₂, where a deflection angle of therotation axis is calculated according to the space linear equation, anda turntable plane is adjusted according to the deflection angle, therebycalibrating the turntable plane and the rotation axis at the same time.

Further, a micro-adjustment mechanism may be mounted on a bottom surfaceof the turntable, the micro-adjustment mechanism may include an X-axisinclinometer and a Y-axis inclinometer that are stacked up and down, andthe X-axis inclinometer and the Y-axis inclinometer may be adjustedaccording to the deflection angle of the rotation axis in step (25) tocalibrate the turntable plane and the rotation axis.

Further, the deflection angle in step (25) may include a deflectionangle

$\alpha = {\arctan\frac{y_{2} - y_{1}}{L_{z}}}$

of the rotation axis in a yoz plane of the data coordinate system, and adeflection angle

$\beta = {\arctan\frac{x_{2} - x_{1}}{L_{z}}}$

of the rotation axis in an xoz plane of the data coordinate system,where x₁ and y₁ are coordinate data of the rotation center point O₁, x₂and y₂ are coordinate data of the rotation center point O₂, and L_(z) isa motion distance of the line structured-light sensor on the Z-axis instep (24).

Further, the calibration on a rotation axis in step (20) may furtherinclude the following step:

(26) moving the line structured-light sensor along the Z-axis of themoving coordinate system, such that the laser plane of the linestructured-light sensor coincides with a horizontal datum plane and thelateral datum plane of the blade, and repeating steps (21)-(24) toobtain rotation center points O₃ and O₄, the rotation center points O₃and O₄ having equal coordinate data x and y, thereby inspecting therotation axis of the blade.

Compared with the prior art, the present disclosure reduces the errorarising from transfer of calibration objects owing to no introduction ofexternal calibration objects, reduces the rotation error because it doesnot involve the rotation angle of the turntable when calibrating therotation axis and the rotation center, and reduces the translationalerror of the line structured-light sensor as positions for rotating theline structured-light sensor in two times are unchanged. Meanwhile, thepresent disclosure calibrates the rotation axis with a high-precisiondatum plane, which not only reduces calibration steps before blademeasurement, but also minimizes a data error after calibration and makesthe measurement on the blade cross-section curve more accurate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified structural schematic diagram of a four-axismeasurement system.

FIG. 2 is a schematic diagram of a positional relationship between aline structured-light sensor and a target measured blade.

FIG. 3 is a structural schematic diagram for acquiring data M₁ of adatum plane A for a first time according to the present disclosure.

FIG. 4 is a structural schematic diagram for acquiring data M₂ of adatum plane A for a second time according to the present disclosure.

FIG. 5 is a structural schematic diagram for acquiring data M₃ of adatum plane A for a third time according to the present disclosure.

FIG. 6 is a schematic diagram of a positional relationship of a linestructured-light sensor on a Z axis in two times by controllingtranslation according to the present disclosure.

FIG. 7 is a schematic diagram of calibration of a rotation axisaccording to the present disclosure.

FIG. 8 is a schematic diagram of a micro-adjustment mechanism accordingto the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiment provides a method for measuring a blade cross-sectionprofile based on a line structured-light sensor at a high precision. Themethod discloses a method for calibrating a rotation axis with a bladeself-feature (a lateral datum plane). Compared with the prior art, thecalibration method achieves a wider serviceable range, and more accuratemeasurement data. Self-features of the blade 200 refer to a lateraldatum plane A201, a datum plane B202 and a horizontal datum plane C203that are machined during machining of the blade 200. The datum planeA201 intersects with the datum plane B202 and is perpendicular to thedatum plane C203. As common features of all blades 200, and having thehigh planeness, the self-features may be viewed as high-precision planefeatures. The method in the embodiment calibrates a rotation center anda rotation axis 300 by using characteristics of either the datum planeA201 or the datum plane B202.

The method for measuring a blade cross-section profile based on a linestructured-light sensor at a high precision provided by the embodimentincludes the following steps:

(10) Calibration on a line structured-light sensor

As shown in FIG. 1, the measurement apparatus includes a linestructured-light sensor 100, a translational drive (S_(X), S_(Y), S_(Z))for controlling motion of the line structured-light sensor within amoving coordinate system O-XYZ, and a rotational drive W for controllingrotation of a turntable 400. The turntable has a rotation centercertainly. There is a need to calibrate a pose of the linestructured-light sensor 100 before installation of the blade 200, toensure the subsequent acquisition accuracy. The calibration method isthe same as the prior art, and will not be repeated in the embodiment.

(20) Calibration on a rotation axis

(21) Put the target measured blade 100 in a center of the turntable, andadjust the pose of the line structured-light sensor 100 by controllingthe translational drive (S_(X), S_(Y), S_(Z)) such that a laser plane ofthe line structured-light sensor 100 intersects with the datum planeA201. As shown in FIG. 2, the blade is provided with two lateral datumplanes A201 and B202 and the horizontal datum plane C203. The embodimentselects the blade datum plane A201, and will use the datum plane B202with the same principles and steps. The embodiment controls thetranslational drive S_(X) to move ΔX₁, the translational drive S_(y) tomove ΔY₁, the translational drive S_(Z) to move ΔZ₁ and the turntable torotate θ, such that laser lines of the line structured-light sensor 100are located on the datum plane A201, and the line structured-lightsensor 100 acquires profile point data M₁ on the datum plane A201, asshown in FIG. 3. Empty points and points not within the datum plane A201are taken as invalid points, and point cloud data

$M_{1} = \begin{bmatrix}{M_{1}x_{1}} & {M_{1}x_{2}} & \ldots & {M_{1}x_{ɛ1}} \\{M_{1}y_{1}} & {M_{1}y_{2}} & \ldots & {M_{1}y_{ɛ1}}\end{bmatrix}$

behind the invalid points is removed.

(22) In order to reduce the error accumulation, ensure that the pose ofthe line structured-light sensor 100 is unchanged, and after theturntable rotates θ, a rotation angle is not too large, and the laserplane of the line structured-light sensor 100 still intersects with thedatum plane A201. As shown in FIG. 3, the line structured-light sensor100 acquires profile point data M₂ of the datum plane A201 again,

$M_{2} = {\begin{bmatrix}{M_{2}x_{1}} & {M_{2}x_{2}} & \ldots & {M_{2}x_{ɛ2}} \\{M_{2}y_{1}} & {M_{2}y_{2}} & \ldots & {M_{2}y_{ɛ2}}\end{bmatrix}.}$

Similarly, rotate the turntable again in a case where the pose of theline structured-light sensor 100 is unchanged, and ensure that the laserplane of the line structured-light sensor 100 still intersects with thedatum plane A201. As shown in FIG. 4, the line structured-light sensor100 acquires profile point data M₃ of the datum plane A201 again

$M_{3} = {\begin{bmatrix}{M_{3}x_{1}} & {M_{3}x_{2}} & \ldots & {M_{3}x_{ɛ3}} \\{M_{3}y_{1}} & {M_{3}y_{2}} & \ldots & {M_{3}y_{ɛ3}}\end{bmatrix}.}$

(23) As the datum plane of the blade has the high linearity, fit thedata M₁, M₂ and M₃ linearly to obtain three straight lines L₁, L₂ andL₃. Since the pose of the line structured-light sensor is unchanged,data coordinate systems for the data M₁, M₂ and M₃ in three timespertain to the same data coordinate system o-xy and thus distances d₁,d₂ and d₃ from the rotation center point O₁ to the three straight linesL₁, L₂ and L₃ are equal. Therefore, the rotation center point O₁ may besolved.

Perform fitting by using a function

${{\min\mspace{11mu}{F\left( {A,B} \right)}} = {\sum\limits_{i = 1}^{ɛ}\left\lbrack {\left( {{Ax}_{i} + B} \right) - y_{i}} \right\rbrack^{2}}},$

(x_(i), y_(i)) being an ith data coordinate in the data M₁, M₂ and M₃,to obtain linear equations of the L₁, L₂ and L₃ in the data coordinatesystem o-xy:

L ₁ :y=A ₁ x+B ₁

L ₂ :y=A ₂ x+B ₂

L ₃ :y=A ₃ x+B ₃

Set the coordinate of the rotation center point O₁ in the datacoordinate system o-xy as (x₁, y₁), then the distances of the threefitting straight lines L₁, L₂ and L₃ to the point O₁ (x₁, y₁) are:

$\left\{ {\begin{matrix}{d_{1} = {\frac{{A_{1}x_{1}} + {B_{1}y_{1}} + C_{1}}{\sqrt{A_{2}^{2} + B_{2}^{2}}}}} \\{d_{2} = {\frac{{A_{2}x_{1}} + {B_{2}y_{1}} + C_{2}}{\sqrt{A_{2}^{2} + B_{2}^{2}}}}} \\{d_{3} = {\frac{{A_{3}x_{1}} + {B_{3}y_{1}} + C_{3}}{\sqrt{A_{2}^{2} + B_{2}^{2}}}}}\end{matrix}\quad} \right.$

The two equations can be combined to solve the coordinate (x₁, y₁) ofthe O₁ point.

With the moving coordinate system O-XYZ when the laser plane of the linestructured-light sensor coincides with the blade datum plane C as anorigin, the coordinate of the O₁ point in the spliced coordinate systemO-XYZ is O₁: (ΔX₁+x₁ ΔY₁+y₁ ΔZ₁), X₁, Y₁ and Z₁ being coordinates in themoving coordinate system O-XYZ when the line structured-light sensoracquires the data M₁.

(24) Move the line structured-light sensor along the Z-axis of themoving coordinate system at a motion distance of L_(Z), as shown in FIG.5, and repeat Steps (21)-(23) to obtain a rotation center point O₂, thecoordinate of the O₂ point in the moving coordinate system O-XYZ beingO₂:(ΔX₁+x₂ ΔY₁+y₂ ΔZ₁+L_(Z)).

(25) As shown in FIG. 6 and FIG. 7, solve a space linear equation of therotation axis through the rotation center points O₁ and O₂:

$\frac{x - {\Delta\; X_{1}} - x_{1}}{x_{2} - x_{1}} = {\frac{y - {\Delta\; Y_{1}} - y_{1}}{y_{2} - y_{1}} = \frac{z - {\Delta\; Z_{1}}}{L_{Z}}}$

With the space linear equation of the rotation axis of the blade 200 inthe spliced coordinate system, the deflection angle of the rotation axisof the blade in the Y′O′Z′ plane may be calculated as

${\alpha = {\arctan\frac{y_{2} - y_{1}}{L_{z}}}},$

and the deflection angle of the rotation axis of the blade in the X′O′Z′plane may be calculated as

$\beta = {\arctan{\frac{x_{2} - x_{1}}{L_{z}}.}}$

Through the micro-adjustment X-axis inclinometer 401 or Y-axisinclinometer 402 under the blade 200, as shown in FIG. 8, the angle ofthe blade is adjusted with the adjustment on R_(X) or R_(Y), such thatthe rotation axis 300 of the blade 200 is located in a verticaldirection.

(26) Move the line structured-light sensor 100 along the Z-axis of themoving coordinate system, such that the laser plane of the linestructured-light sensor 100 coincides with the horizontal datum planeand the lateral datum plane of the blade, and repeat Steps (21)-(24) toobtain rotation center points O₃ and O₄, the rotation center points O₃and O₄ having equal coordinate data (x, y), thereby inspecting therotation axis of the blade.

(30) Measurement on a target measured blade

(31) Establish a global coordinate system O-XYZ, with an intersectionpoint between a datum plane C of the target measured blade and therotation axis as an origin O, two normal vectors perpendicular to eachother on the datum plane C as X and Y axes, and the rotation axis as a Zaxis.

(32) Acquire data at different positions of the target measured blade200 by moving the line structured-light sensor 100 and rotating theturntable, and convert the acquired data to the global coordinate systemO-XYZ for data splicing, thereby implementing the measurement on aprofile of the target measured blade.

Of note, the terminology used herein is for the purpose of describingparticular embodiments only and is not intended to be limiting of theinvention. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“includes”, and/or “including,” when used in this specification, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

As well, the corresponding structures, materials, acts, and equivalentsof all means or step plus function elements in the claims below areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

Having thus described the invention of the present application in detailand by reference to embodiments thereof, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims as follows:

What is claimed is:
 1. A method for measuring a blade cross-sectionprofile based on a line structured-light sensor at a high precision,comprising the following steps: (10) a step of pose calibration on aline structured-light sensor: calibrating X, Y and Z axes of a movingcoordinate system, such that a data coordinate system o-xyz of the linestructured-light sensor is parallel to the moving coordinate systemO-XYZ; (20) a step of calibration on a rotation axis: calibrating therotation axis of a turntable, such that a blade axis is parallel to therotation axis; and (30) a step of cross-section profile measurement on atarget measured blade: establishing a global coordinate system, andconverting blade cross-section curve feature data acquired by the datacoordinate system to the coordinate system for splicing, therebymeasuring a blade cross-section profile; wherein the calibration on arotation axis in step (20) comprises the following steps: (21) puttingthe target measured blade onto the turntable, and adjusting a pose ofthe line structured-light sensor such that a laser plane of the linestructured-light sensor intersects with a lateral datum plane of theblade, the line structured-light sensor acquiring profile point data M₁of the datum plane; (22) ensuring that the pose of the linestructured-light sensor is unchanged, and the line structured-lightsensor acquires profile point data M₂ of a lateral datum plane afterrotation of the turntable; and rotating the turntable again and ensuringthat the pose of the line structured-light sensor is unchanged, and theline structured-light sensor acquires profile point data M₃ of thelateral datum plane, wherein the lateral datum planes in step (21) andstep (22) are the same datum plane; (23) fitting the data M₁, M₂ and M₃linearly to obtain three straight lines L₁, L₂ and L₃, and solving,according to equal distances from a rotation center point O₁ to thethree straight lines L₁, L₂ and L₃, the rotation center point O₁; (24)moving the line structured-light sensor along the Z-axis of the movingcoordinate system, such that the laser plane of the linestructured-light sensor intersects with the lateral datum plane of theblade, and repeating steps (21)-(23) to obtain a rotation center pointO₂; and (25) solving a space linear equation of the rotation axisthrough the rotation center points O₁ and O₂, wherein a deflection angleof the rotation axis is calculated according to the space linearequation, and a turntable plane is adjusted according to the deflectionangle, thereby calibrating the turntable plane and the rotation axis atthe same time.
 2. The method for measuring a blade cross-section profilebased on a line structured-light sensor at a high precision according toclaim 1, wherein a micro-adjustment mechanism is mounted on a bottomsurface of the turntable, the micro-adjustment mechanism comprises anX-axis inclinometer and a Y-axis inclinometer that are stacked up anddown, and the X-axis inclinometer and the Y-axis inclinometer areadjusted according to the deflection angle of the rotation axis in step(25) to calibrate the turntable plane and the rotation axis.
 3. Themethod for measuring a blade cross-section profile based on a linestructured-light sensor at a high precision according to claim 1,wherein the deflection angle in step (25) comprises a deflection angle$\alpha = {\arctan\frac{y_{2} - y_{1}}{L_{z}}}$ of the rotation axis ina yoz plane of the data coordinate system, and a deflection angle$\beta = {\arctan\frac{x_{2} - x_{1}}{L_{z}}}$ of the rotation axis inan xoz plane of the data coordinate system, wherein x₁ and y₁ arecoordinate data of the rotation center point O₁, x₂ and y₂ arecoordinate data of the rotation center point O₂, and L_(z) is a motiondistance of the line structured-light sensor on the Z-axis in step (24).4. The method for measuring a blade cross-section profile based on aline structured-light sensor at a high precision according to claim 2,wherein the deflection angle in step (25) comprises a deflection angle$\alpha = {\arctan\frac{y_{2} - y_{1}}{L_{z}}}$ of the rotation axis ina yoz plane of the data coordinate system, and a deflection angle$\beta = {\arctan\frac{x_{2} - x_{1}}{L_{z}}}$ of the rotation axis inan xoz plane of the data coordinate system, wherein x₁ and y₁ arecoordinate data of the rotation center point O₁, x₂ and y₂ arecoordinate data of the rotation center point O₂, and L_(z) is a motiondistance of the line structured-light sensor on the Z-axis in step (24).5. The method for measuring a blade cross-section profile based on aline structured-light sensor at a high precision according to claim 1,wherein the calibration on a rotation axis in step (20) furthercomprises the following step: (26) moving the line structured-lightsensor along the Z-axis of the moving coordinate system, such that thelaser plane of the line structured-light sensor coincides with ahorizontal datum plane and the lateral datum plane of the blade, andrepeating steps (21)-(24) to obtain rotation center points O₃ and O₄,the rotation center points O₃ and O₄ having equal coordinate data x andy, thereby inspecting the rotation axis of the blade.